i have a question:
exists any system call for generate a core dump?
I know which a core dump could be generated by a signal, but i want know if it's possible generated from system call
void createdump(void)
{
if(!fork()) { //child process
// Crash the app
abort() || (*((void*)0) = 42);
}
}
What ever place you wan't to dump call the function. This will create a child and crash it. So you can get dump even without exiting your program
You can also raise the SIGABRT signal to get the core dump.
raise(SIGABRT);
*this is equivalent to calling abort() directly.
Same idea as code hacker's answer, but compilable, with error handling, and without the zombie:
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
int
coredump(void)
{
pid_t p,r;
if(0>(p=fork()))
return -1;
if(0==p)
abort() /*child*/;
/*reap zombie*/
do r=waitpid(p,0,0); while(0>r && EINTR==errno);
if(0>r) {
perror("waitpid shouldn't have failed");
abort();
}
return 0;
}
This still has the rather obvious deficiency in that that it won't work with multithreaded processes.
Related
I am currently facing issue with the glibc v2.22 where I am not able to get the proper unwind information.
When there is SIGABRT application, it is calling abort function from glibc. It should be using unwind information which is enabled in the build. However, it is scanning the stack (as indicated by the red line below the address in the screenshot) and providing the misleading information as shown in the screenshot attached (using sentry for analyzing the dump).
Here, do_crash is called which does assert(0) which then aborts the main application. While analyzing the dump, the do_crash function calls the _fini which is never in the main application's stack.
I have enabled unwind for the glibc by using CFLAGS += "-funwind-tables". I also tried with the flags such as -rdynamic and -fno-omit-frame-pointer but it was also of no use.
Am I missing something here? How can I get the complete backtrace of the signals, particularly SIGABRT?
Thanks in advance
When there is SIGABRT application, it is calling abort function from glibc
That is not true, this is not happening, unless you explicitly registered it.
I have enabled unwind for the glibc by using CFLAGS += "-funwind-tables"
It tells the compiler to add the information, it doesn't "enable unwind". What exactly happens when compiling with -funwind-tables?
Here, do_crash is called which does assert(0) which then aborts the main application.
This is not related to receiving SIGABRT signal.
Am I missing something here?
I believe you are making wrong assumptions - that something is called on SIGABRT, that SIGABRT is sent on assert, that abort() is called on SIGABRT. Nothing is called on SIGABRT and the program is terminated when receiving SIGABRT by default (see man 7 signal), assert just terminates the program and doesn't raise SIGABRT, and abort() raises the SIGABRT signal, not receives it.
How can I get the complete backtrace of the signals, particularly SIGABRT?
Register a handler that will do that. See How to automatically generate a stacktrace when my program crashes .
#include <execinfo.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
void handler(int sig) {
void *array[10];
size_t size;
size = backtrace(array, 10);
backtrace_symbols_fd(array, size, STDERR_FILENO);
_Exit(1);
}
int main(int argc, char **argv) {
signal(SIGABRT, handler); // install our handler
raise(SIGABRT);
}
If you want to print stacktrace on assert() that's completely different and you would overwrite the glibc handler for assert to do that:
#include <assert.h>
#include <execinfo.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
void print_trace(void) {
void *array[10];
size_t size;
size = backtrace(array, 10);
backtrace_symbols_fd(array, size, STDERR_FILENO);
}
// based on https://code.woboq.org/userspace/glibc/assert/assert.c.html
void __assert_fail(const char *assertion, const char *file, unsigned int line, const char *function) {
extern const char *__progname;
fprintf(stderr, "%s%s%s:%u: %s%sAssertion `%s' failed.\n",
__progname, __progname[0] ? ": " : "",
file, line,
function ? function : "", function ? ": " : "",
assertion);
print_trace();
abort();
}
int main() {
assert(0);
}
I'm trying to debug a linux user-space application, which creates a process group with setpgid(0,0). When launched on terminal, it returns no error and work as expected. But when debugging with gdb, it returns EPERM.
I suspect that it is because the gdb attaches my process as a child. So it is not possible to set my process as parent with setpgid(0,0). Is that correct? If so, isn't there a way to debug this case with gdb?
Edit:
Environment:
Ubuntu 12.04 Kernel 3.11.0-15-generic
Using the simple code below, if launched on terminal, I get success!!. If I debug with gdb (configured on Eclipse Luna), I get setpgid: Operation not permitted.
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main()
{
int err = setpgid((pid_t)0, (pid_t) 0);
if (err < 0)
perror("setpgid");
else
printf("success!! \n");
exit(err);
}
I am looking for a ptrace() call to observe a process until the process exits.
I have this which compiles with gcc / cc on OSX:
#include <sys/types.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <stdio.h>
#include <sys/ptrace.h>
int main(int argc, char *argv[]) {
pid_t pidx = atoi(argv[1]);
printf("pid = %jd\n", (intmax_t) pidx);
ptrace(PT_ATTACHEXC, pidx, 0, 0);
wait(NULL);
}
However, even with a valid/existing pid, this program will still exit immediately. I am trying to only exit this program after pidx dies.
Is this possible somehow?
Ideally I want something that works on both OSX and Linux.
Your problem is probably that the wait call returns immediately, because the traced "inferior" process is suspended, you know, waiting for you to debug it. You're going to need some kind of loop in which you make ptrace requests to inspect the child and then resume execution, and then call wait again to wait for it to suspend on the next breakpoint or whatever. Unfortunately the debugger API is extremely non-portable; you will have to write most of this program twice, once for OSX and once for Linux.
I'm a beginner programmer to C and I'm trying to write a basic shell. I'm trying to use the fork() function, but it simply doesn't seem to work. I get caught in an endless loop of just my shell's prompt taking input and then seemingly doing nothing with it.
I ran the debugger and set the breakpoint to where the program forks, and at that point, I got an error message of
Can't find a source file at "/build/glibc-Cl5G7W/glibc-2.23/posix/../sysdeps/nptl/fork.c"
Locate the file or edit the source lookup path to include its location.
What I think is happening is that I either messed up with my #include headers or that when I tried to compile, I left some library out. I've just been compiling with the standard
gcc -o shell custom_shell.c
and I recall my teacher saying something about compiling with libraries, but I thought my #include headers would cover that and I can't find anything else on the topic online.
The parts of my code I'm wary over are
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
...
pid_t pid = fork();
if (pid < 0){ //error
perror("fork");
exit(1);
}
else if (pid == 0){ //child
execvp(args[0], args);
}
else{ //parent
wait(0);
}
I was working on my project when I needed to use "curl" to obtain some data from www. Now firstly I tried direct system() function but it didn't worked, strangely everytime it corrupted the whole source code file while compiling with gcc. Luckily I was testing it separately.
Then I tested execl() function, this code compiles OK and gcc gives me a .exe file to run, but nothing happens when I run it,blank windows appears. CODE:
int main(){
execl("curl","curl","http://livechat.rediff.com/sports/score/score.txt",">blahblah.txt",NULL);
getch();
return 0;
}
Includes are not shown properly but I have included stdio,conio,stdlib and unistd.h.
How can I get output of program to store in text file? Also running the above command creates and stores text file in My Documents, I want it to be in local directory from where I run the program. How can I do that?
You need to provide the path of curl, and you cannot use redirection because the application will not be executed through bash. Instead use the -o flag and specify the filename. Also, execl does not return when successful:
#include <unistd.h>
#include <stdio.h>
int main(){
execl("/usr/bin/curl",
"curl","http://livechat.rediff.com/sports/score/score.txt",
"-oblahblah.txt",NULL
);
printf("error\n");
return 0;
}
If you want your code to return, you should fork a child process to run the command. This way you can check the return code.
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#define CURL "/usr/bin/curl"
int main()
{
pid_t pid;
int status;
pid = fork();
if (pid == 0)
{
execl(CURL, CURL, arg1, NULL);
}
else if (pid < 0)
{
printf("Fork failed\n");
exit (1);
}
else
{
if (waitpid(pid, &status, 0) != pid)
status = -1;
}
return status;
}
arg1 is whatever argument you want to use with curl or if you aren't using any than you obviously can omit it.